The present invention relates to a method of determining a flag state of a non-volatile memory device.
In recent years, there has been an increasing demand for non-volatile memory devices which can be electrically programmed and erased and do not need a refresh function of rewriting data at specific intervals.
A non-volatile memory device generally includes a memory cell array in which cells for storing data are arranged in matrix form, and a page buffer for writing memory into specific cells of the memory cell array or reading memory stored in a specific cell. The page buffer includes a bit line pair connected to a specific memory cell, a register for temporarily storing data to be written into the memory cell array or reading data of a specific cell from the memory cell array and temporarily storing the read data, a sense node for sensing the voltage level of a specific bit line or a specific register, and a bit line select unit for controlling whether the specific bit line is connected to the sense node.
In a multi-level cell (MLC) programming method, 2-bit or more data can be stored in one cell. A number of program operations, such as a least significant bit (LSB) programming operation and a most significant bit (MSB) programming operation, are performed. It is necessary to check whether a current programmed state is a LSB program or an MSB program. For this purpose, an additional cell called a flag cell is used to check a programmed state.
The flag cell is connected to the same word line as that of a main cell to be programmed and is subject to a program operation in the same manner as the main cell. The flag cell typically includes a plurality of cells. The programmed state of a main cell is determined depending on how many cells of a plurality of cells have been programmed to have a threshold voltage higher than a specific voltage.
An additional circuit is constructed in order to determine whether a flag cell is programmed. Thus, there is a need to reduce the occupied area of a chip by removing the flag cell.